Removed both fuel coolers(twin engines).
Both failed.
Would be looking for a different design i would think.
Anyone with these coolers if you havn't already done so should maybe inspect/test and replace.
Rob

Look at your fuel system, make sure that there is no way for the return flow to the tank to be blocked. If that flow is blocked, pressure in cooler can go sky-high and collapse it internally. A simple valve misposition can do it, or if a non-return fitting is accidentally used in the return path.

What do insides of fuel cooler look like? Any deformation? Usually the Cummins coolers are pretty reliable, although there have been occasional failures.

If both failed, chances of both being a random failure seem low. Worthwhile to look for a common cause.

Look at your fuel system, make sure that there is no way for the return flow to the tank to be blocked. If that flow is blocked, pressure in cooler can go sky-high and collapse it internally. A simple valve misposition can do it, or if a non-return fitting is accidentally used in the return path.

What do insides of fuel cooler look like? Any deformation? Usually the Cummins coolers are pretty reliable, although there have been occasional failures.

If both failed, chances of both being a random failure seem low. Worthwhile to look for a common cause.

Hi Ski
Thanks again for your great info.
Will run the return lines into a bucket tomorrow to see if we have good flow.
I have gone out and bought a different heat exchanger a Bowman 31 982, this is a tube bundle type. I was a bit concerned that this would not give the correct flow but the guy at the shop gauranteed it would.
Will test tomorrow.
Raw water is delivered by Jets and there was no visable signs of damage to the insides of the coolers.
Rob

Not concerned about return flow from engine as would be determined by bucket test, concerned about whether flow from engine could be blocked on its way to tank. More of a plumbing issue than engine issue.

Usually if this happens, cooler fuel passage inside tube collapses, which is visually obvious. So not likely your issue.

Please excuse me for the thread hijack but what is the purpose of a fuel cooler? (ok the name says all, to cool the fuel of course). I mean I thought it was better for diesel fuel to be warm as more fluid and better for injector "mist".
Ski may you give me some light on this and decrease my ignorance

Lou,
Many turbo engines that are expected to run hard and long times use a fuel cooler. When fuel transits the injection pump, and injectors it picks up heat. That heat will expand the fuel to the point that the engine gets a sufficiently less dense fuel charge that the engine cannot make its rated HP. The fuel coolers take that heat away.
Often takes the fuel to reach approx. 140F to be a problem but it can happen on engines working hard or long enough and with tanks not large enough to dissipate that heat readily.
My own engine, a natural, heats the fuel. The return lines are darn warm and at the end of a day's run the whole tank is noticeably warmer.